Parkinson's disease (PD) is a chronic, progressive disease usually affecting people over the age of 65, a segment of the United States population that is rapidly expanding. The broad goal of this proposal is to understand the preparatory cortical mechanisms that underlie response to postural perturbation in healthy individuals and how this preparatory activity is impaired in adults with PD. More specifically, electroencephalography (EEG) will be used to measure contingent negative variation (CNV), a slow, negative shift in EEG amplitude that occurs prior to cued voluntary movements. The CNV measures preparatory cortical activity and reflects 'central set'and anticipatory preparation of responses. Previous studies have shown that PD affects 'central set'and postural responses, but have not measured corresponding cortical activity. The hypothesis of this proposal is that preparatory cortical activity represents 'central set'for anticipatory scaling of postural responses and that PD affects this 'central set'. The first aim is to compare preparatory cortical potentials prior to predictable and unpredictable magnitudes of postural perturbations in healthy individuals, testing the hypothesis that the role of anticipatory cortical activity is to scale postural responses for the anticipated magnitude of perturbations. It is proposed that healthy adult participants will show larger amplitude CNVs in their EEG prior to predictable magnitude perturbations than to unpredictable perturbations. It is also hypothesized that there will be larger amplitude CNVs before large, predictable perturbations than before small, predictable perturbations requiring a smaller postural response. The second aim is to compare preparatory cortical potentials prior to predictable and unpredictable magnitudes of postural perturbations in adults with PD to age-matched, healthy individuals. Adults with PD show impaired anticipatory scaling behaviorally, as compared to healthy adults. The hypothesis is that adults with PD will show smaller amplitude CNV as compared to healthy controls. The third aim is to compare how "Think Big", an attentional cuing strategy, affects preparatory cortical potentials and the size of predictable postural responses. It is hypothesized that instructing adults with PD to "think big" prior to receiving a postural perturbation will increase both the amplitude of the CNV and the size of the postural response. These studies will support focused rehabilitation approaches to improve postural control and decrease falls in adults with Parkinson's disease by providing a better understanding of how 1) cortical preparation is related to 'central set'for postural control, 2) PD affects 'central set'and CNV function and 3) cuing alters CNV function and postural responses in PD. PUBLIC HEALTH RELEVANCE: In the United States, it is estimated that 60,000 new cases of Parkinson's disease (PD) are diagnosed each year, joining the 1 million Americans who currently have PD. Although medications help with many symptoms of PD, they do not stop disease progression and are not beneficial for posture, balance and gait problems associated with PD. A better understanding of how PD affects the ability to prepare responses for anticipated postural perturbations is needed before effective rehabilitation interventions can be developed for adults with PD.